emacs-version
"27.0.50"

system-type
darwin

(frame-list-z-order)
(#<frame *scratch* "~/" 0x104ae0d38> #<frame TAGS<bk> "/Users/bk/"
0x1015f3e48> #<frame *Help* "~/" 0x1014b8000> #<frame TAGS<bk> "/Users/bk/"
0x11f959e40> #<frame TAGS<bk> "/Users/bk/" 0x101564fb0> 2111061947183245)

(x-display-list)
("bka-iMac.local")

;; Result should be the same as frame-list-z-order called without an
;; argument since we have only 1 display connection, but it isn't.
(frame-list-z-order (car (x-display-list)))
nil